Release sheet

ABSTRACT

A release sheet comprising a base material and a release agent layer formed on at least one surface of the base material, wherein: the release agent layer is formed by using a release agent composition; the release agent composition contains a first polydimethylsiloxane having at least two alkenyl groups in one molecule and a second polydimethylsiloxane having at least two hydrosilyl groups in one molecule; the release agent composition contains 10.00 to 16.00 mmol of the alkenyl groups and 40.00 to 145.00 mmol of the hydrosilyl groups in a total of 30 g of the first polydimethylsiloxane and the second polydimethylsiloxane; and a molar ratio (b/a) of the hydrosilyl groups (b) to the alkenyl groups (a) is 2.0 to 15.0. According to the release sheet, it is possible to suppress the peeling force from increasing even when the release agent layer of the release sheet is exposed to the air for a long time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application ofPCT/JP2012/083127 filed on Dec. 20, 2012, and claims priority to, andincorporates by reference, Japanese Patent Application No. 2012-071912filed on Mar. 27, 2012.

TECHNICAL FIELD

The present invention relates to a release sheet on which a pressuresensitive adhesive layer of a pressure sensitive adhesive sheet or thelike is laminated.

BACKGROUND ART

For a pressure sensitive adhesive sheet, a release sheet is generallyused which comprises a base material and a release agent layer formed onone surface of the base material (e.g., Patent Literature 1). Many ofrelease sheets for a pressure sensitive adhesive sheet are usually usedsuch that, after a pressure sensitive adhesive is coated and dried on asubstrate which is being carried in a roll-to-roll manner, the releaseagent layer surface of the release sheet is attached to the surface ofthe obtained pressure sensitive adhesive layer. When a pressuresensitive adhesive sheet is produced in a roll-to-roll manner, thecarrying speed from the roll may be constant, so that the release sheetis unlikely to be exposed to the air for a long time. As for the releasesheet, in a pre-process of attaching the pressure sensitive adhesivelayer of the pressure sensitive adhesive sheet and the release agentlayer of the release sheet together, back-split processing (cut orhalf-cut) or the like may be performed for the release sheet.

When the processing as the above is performed, the release agent layerof the release sheet may be exposed to the air for a long time. If therelease agent layer of the release sheet is exposed to the air for along time in this way, there is a problem in that the peeling force ofthe release agent layer from the pressure sensitive adhesive layerbecomes larger than that before the exposure to the air. In particular,as the peeling force increases such as in a sheet having tightreleasability, the increase in the peeling force due to exposure to theair tends to be remarkable.

The increased peeling force of the release sheet as the above may causerelease failure to occur when the release sheet is peeled off from thepressure sensitive adhesive sheet after the pressure sensitive adhesivelayer of the pressure sensitive adhesive sheet and the release agentlayer of the release sheet are attached together.

PRIOR ART LITERATURE Patent Literature

[Patent Literature 1] JP2002-363515A

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The reason for the above increased peeling force due to exposure to theair is not necessarily sure, but this is considered to be mainly becausedust and dirt or the like contained in the air become attached to therelease agent layer.

The present invention has been made in consideration of such actualcircumstances, and an object of the present invention is to provide arelease sheet which can suppress the peeling force from increasing evenwhen the release agent layer of the release sheet is exposed to the airfor a long time.

Means for Solving the Problems

To achieve the above object, the present invention provides a releasesheet comprising a base material and a release agent layer formed on atleast one surface of the base material, the release sheet beingcharacterized in that: the release agent layer is formed using a releaseagent composition; the release agent composition contains a firstpolydimethylsiloxane having at least two alkenyl groups in one moleculeand a second polydimethylsiloxane having at least two hydrosilyl groupsin one molecule; the release agent composition contains 10.00 to 16.00mmol of the alkenyl groups and 40.00 to 145.00 mmol of the hydrosilylgroups in a total of 30 g of the first polydimethylsiloxane and thesecond polydimethylsiloxane; and a molar ratio (b/a) of the hydrosilylgroups (b) to the alkenyl groups (a) is 2.0 to 15.0 (Invention 1).

According to the above invention (Invention 1), it is possible tosuppress the peeling force from increasing thereby to reduce releasefailure at the time of peeling off the release sheet from a pressuresensitive adhesive sheet even when the release agent layer of therelease sheet is exposed to the air for a long time.

In the above invention (Invention 1), it is preferable that aweight-average molecular weight of the first polydimethylsiloxane is200,000 to 1,300,000 and a weight-average molecular weight of the secondpolydimethylsiloxane is 300 to 1,200 (Invention 2).

In the above invention (Inventions 1, 2), it is preferable that therelease agent composition further contains a platinum-group metal-basedcompound as a catalyst (Invention 3).

In the above invention (Inventions 1 to 3), it is preferable that apeeling force rate of change represented by {(peeling force Y−peelingforce X)/peeling force X}×100 is 30% or less, where the peeling force Xis a 180° peeling force (mN/20 mm) of a polyester pressure sensitiveadhesive tape No. 31B available from Nitto Denko Corporation from therelease sheet in a state of no exposure to air, and the peeling force Yis a 180° peeling force (mN/20 mm) of a polyester pressure sensitiveadhesive tape No. 31B available from Nitto Denko Corporation from therelease sheet which has been exposed to air for 7 days in a clean roomunder a condition of class 10,000 (ISO class 7), a temperature of 23° C.and a humidity of 50% RH (Invention 4).

Advantageous Effect of the Invention

According to the release sheet of the present invention, it is possibleto suppress the peeling force from increasing even when the releaseagent layer of the release sheet is exposed to the air for a long time.This reduces release failure at the time of peeling off the releasesheet from a pressure sensitive adhesive sheet.

BRIEF DESCRIPTION OF DRAWING(S)

FIG. 1 is a cross-sectional view of a release sheet according to oneembodiment of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will hereinafter be described.

As shown in FIG. 1, a release sheet 1 according to the presentembodiment is configured to comprise a base material 11 and a releaseagent layer 12 formed on one surface of the base material 11.

The base material 11 to be used is not particularly limited, and mayappropriately be selected from any of conventionally known ones.Examples of such base material 11 include a film formed of plastic, suchas polyethylene terephthalate, polyethylene naphthalate and otherpolyester, polypropylene, polymethylpentene and other polyolefin,polycarbonate, and polyvinyl acetate, which may be a single layer, ormay be multilayer of two or more layers of the same type or differenttypes. Among them, a polyester film is preferable, a polyethyleneterephthalate film is more preferable, and a biaxial stretchedpolyethylene terephthalate film is most preferable.

If necessary, either one surface or both surfaces of the base material11 comprising a film as described above may be subjected to surfacetreatment such as using oxidation method and roughening method or primertreatment for the purpose of improving the interfacial adhesion with therelease agent layer 12 to be provided on the surface. Examples of theabove oxidation method include corona discharge treatment, plasmadischarge treatment, chromium oxidation treatment (wet type), flametreatment, hot-air treatment, ozone exposure treatment, and ultravioletirradiation treatment. Examples of the roughening method includesandblasting method and thermal spraying method. These surface treatmentmethods may be appropriately selected depending on the type of the basematerial film, and the corona discharge treatment method may preferablybe used in view of the effect and the operability in general.

Other than the film as described above, papers such as glassine paper,clay-coated paper, resin-coated paper and laminated paper (such aspolyethylene laminated paper and polypropylene laminated paper),non-woven cloth, metal foil and the like may also be used as the basematerial 11.

The thickness of the base material 11 may ordinarily be 10 to 300 μm,preferably 15 to 200 μm, and particularly preferably 20 to 125 μm.

The release agent layer 12 in the present embodiment is formed using arelease agent composition as below. The release agent composition in thepresent embodiment contains, as addition reaction-type silicone resins,a first polydimethylsiloxane having at least two alkenyl groups in onemolecule and a second polydimethylsiloxane having at least twohydrosilyl groups in one molecule.

Examples of the alkenyl groups contained in the firstpolydimethylsiloxane include monovalent hydrocarbon groups such as vinylgroup, allyl group, propenyl group, butenyl group, pentenyl group,hexenyl group, heptenyl group and octenyl group, among which vinyl groupis particularly preferable.

A total of 30 g of the first polydimethylsiloxane and the secondpolydimethylsiloxane contains 10.00 to 16.00 mmol of the alkenyl groups,and may preferably contain 11.00 to 15.80 mmol of the alkenyl groups. Atotal of 30 g of the first polydimethylsiloxane and the secondpolydimethylsiloxane contains 40.00 to 145.00 mmol of the hydrosilylgroups, and may preferably contain 43.00 to 142.00 mmol of thehydrosilyl groups. A molar ratio (b/a) of the hydrosilyl groups (b) tothe alkenyl groups (a) is 2.0 to 15.0, and may preferably be 2.5 to13.0.

By forming the release agent layer 12 using a release agent compositionthat satisfies the above conditions, the release agent layer 12 issuppressed from increasing the peeling force even when the release agentlayer 12 is exposed to the air for a long time. The reason for this isnot necessarily sure, but this is considered to be because the releaseagent layer 12 formed using the release agent composition satisfying theabove conditions has a low polarity, so that dust and dirt or the like,which have a high polarity, are unlikely to attach to the release agentlayer 12.

When the amount of the alkenyl groups is less than 0.40 mmol or if theamount of the hydrosilyl groups is less than 7.00 mmol in a total of 30g of the first polydimethylsiloxane and the second polydimethylsiloxane,insufficient curing of the release agent composition may occur to leadto a problem in that the silicone transfers to a coating machine, thepressure sensitive adhesive layer of the pressure sensitive adhesivesheet and the like, and further the releasability will be affected.

If, on the other hand, the relation of the molar ratio (b/a) of thehydrosilyl groups (b) to the alkenyl groups (a) in the total of 30 g ofthe first polydimethylsiloxane and the second polydimethylsiloxane isnot within the above range, there may occur a problem in that thepeeling force of the release agent layer 12 from the pressure sensitiveadhesive layer becomes larger than that before exposure to the air undera condition where the release sheet 1 is exposed to the air for a longtime. If the adding amount of the second polydimethylsiloxane of a lowmolecular weight having the hydrosilyl groups is large, the viscosity ofthe coating liquid decreases, so that there may be a problem in thatcissing occurs at the coating surface of the release agent when therelease sheet 1 is manufactured, and a problem in that the pressuresensitive adhesive is cohesive failure and/or transferred to the side ofthe release sheet 1 because the peeling force of the release agent layer12 from the pressure sensitive adhesive layer becomes large.

The first polydimethylsiloxane may preferably contain no hydrosilylgroup, and the second polydimethylsiloxane may preferably contain noalkenyl group.

The weight-average molecular weight of the first polydimethylsiloxanemay preferably be 20,000 to 1,300,000, and particularly preferably300,000 to 1,200,000. The weight-average molecular weight of the secondpolydimethylsiloxane may preferably be 300 to 1,400, and particularlypreferably 500 to 1,200. The weight-average molecular weight as usedherein is a converted value in terms of polystyrene measured by using agel permeation chromatography (GPC) method.

The above release agent composition may preferably contain a catalyst.The catalyst is not particularly limited so long as it can cure therelease agent composition according to the present embodiment, but aplatinum-group metal-based compound may be preferable. Examples of theplatinum-group metal-based compound include fine particle-like platinum,fine particle-like platinum adsorbed on carbon powder carrier,chloroplatinic acid, alcohol modified chloroplatinic acid, olefincomplex of chloroplatinic acid, palladium, and rhodium. The releaseagent composition may contain such a catalyst thereby allowing to moreefficiently progress the curing reaction of the release agentcomposition.

It may be preferable that the content of the catalyst in the aboverelease agent composition is about 1 to 1,000 ppm with respect to thetotal amount of components other than the catalyst.

The above release agent composition may contain reaction inhibitor,adhesion improving agent or the like in addition to the firstpolydimethylsiloxane, the second polydimethylsiloxane and the catalyst.

The thickness (basis weight) of the release agent layer 12 is notparticularly limited but may preferably be 0.01 to 3 g/m², andparticularly preferably 0.05 to 2 g/m². If the thickness of the releaseagent layer 12 is less than 0.01 g/m², the functionality as the releaseagent layer 12 may not be sufficiently brought out depending onmaterials that constitute the release agent layer 12, etc. If thethickness of the release agent layer 12 exceeds 3 g/m², blocking mayoccur when the release sheet 1 is wound in a roll form, possiblyresulting in some troubles at the time of unwinding.

The release agent layer 12 can be formed by applying a coating liquid,which contains the release agent composition and a desired diluent, toone surface of the base material 11 and thereafter drying the coatingliquid and curing it. Examples of coating method to be used includegravure-coating method, bar-coating method, spray-coating method,spin-coating method, knife-coating method, roll-coating method, anddie-coating method.

The above diluent is not particularly limited, and various types may beused. Examples of the diluents include hydrocarbon compounds, such astoluene, hexane and heptane, as well as acetone, ethyl acetate, methylethyl ketone, methyl isobutyl ketone, and mixture thereof.

It may be preferable that the release agent composition coated in theabove manner is thermally cured. In this case, the heating temperaturemay preferably be 80° C. to 180° C., and the heating time may preferablybe about 10 to 90 seconds.

As previously described, according to the release sheet 1 of the presentembodiment, it is possible to suppress the peeling force from increasingeven when the release agent layer 12 of the release sheet 1 is exposedto the air for a long time. Specifically, a peeling force rate of changerepresented by

{(peeling force Y−peeling force X)/peeling force X}×100 may preferablybe 30% or less, particularly preferably 25% or less, further preferably15% or less, and most preferably 10% or less,

where the peeling force X is a 180° peeling force (mN/20 mm) of apolyester pressure sensitive adhesive tape No. 31B available from NittoDenko Corporation from the release sheet 1 in a state of no exposure tothe air, and

the peeling force Y is a 180° peeling force (mN/20 mm) of a polyesterpressure sensitive adhesive tape No. 31B available from Nitto DenkoCorporation from the release sheet 1 which has been exposed to the airfor 7 days in a clean room under a condition of class 10,000 (ISO class7), a temperature of 23° C. and a humidity of 50% RH. In order that thepeeling force is not unduly reduced, the peeling force rate of changemay preferably be −30% or more.

In the above clean room, the release sheet 1 is to be suspended in thevertical direction to the ground surface when the release sheet 1 isexposed to the air. If the exposure is such that the release sheet 1 isnot suspended in the vertical direction to the ground surface, there maybe a possibility that the measurement of the peeling force is affectedby dust or dirt when the dust or dirt is deposited on the surface of therelease agent layer 12, so that the peeling force is unstable, becausesome dust and dirt are present even in a clean room.

The peeling force rate of change of the release sheet 1 may be the abovevalue or less thereby to reduce the release failure when the releasesheet 1 is peeled off from the pressure sensitive adhesive sheet afterthe pressure sensitive adhesive layer of the pressure sensitive adhesivesheet and the release agent layer 12 of the release sheet 1 are attachedtogether.

It should be appreciated that the embodiments heretofore explained aredescribed to facilitate understanding of the present invention and arenot described to limit the present invention. Therefore, it is intendedthat the elements disclosed in the above embodiments include all designchanges and equivalents to fall within the technical scope of thepresent invention.

For example, one or more other layers such as an antistatic layer may beprovided on the opposite surface to the release agent layer 12 of thebase material 11 and/or between the base material 11 and the releaseagent layer 12.

EXAMPLES

The present invention will hereinafter be described further specificallywith reference to examples, etc, but the scope of the present inventionis not limited to these examples, etc.

Example 1

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin (weight-average molecular weight: 10,000), was prepared as anaddition reaction-type organopolysiloxane (release agent composition A)having a weight-average molecular weight of 501,000. The release agentcomposition A was diluted using toluene so that the solid content wouldbe 30 mass %, and a silicone resin solution was thus prepared. A coatingliquid was obtained by adding 2 mass parts of a platinum-based catalyst(BY24-835 available from Dow Corning Toray Co., Ltd.) to 100 mass partsof that silicone resin solution and performing adjustment using toluenesuch that the concentration of the solid content would be 1.5 mass %.

The obtained coating liquid was uniformly applied to a polyethyleneterephthalate film (T-100 available from Mitsubishi Plastics, Inc.,thickness of 38 μm) as the base material by means of a bar-coatingmethod so that the film thickness after drying would be a basis weightof 0.09 g/m², and thereafter dried at 130° C. for 1 minute. A releasesheet having a release agent layer laminated on the base material wasthereby obtained such that the release agent layer was covered by thebase material so as not to be exposed to the air.

Example 2

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin (weight-average molecular weight: 10,000), was prepared as anaddition reaction-type organopolysiloxane (release agent composition B)having a weight-average molecular weight of 583,000. A release sheet wasproduced in the same manner in Example 1 except that the release agentcomposition B was used in place of the release agent composition A inExample 1.

Example 3

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin, was prepared as an addition reaction-type organopolysiloxane(release agent composition C) having a weight-average molecular weightof 634,000. A release sheet was produced in the same manner in Example 1except that the release agent composition C was used in place of therelease agent composition A in Example 1.

Example 4

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin, was prepared as an addition reaction-type organopolysiloxane(release agent composition D) having a weight-average molecular weightof 658,000. A release sheet was produced in the same manner in Example 1except that the release agent composition D was used in place of therelease agent composition A in Example 1.

Example 5

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin, was prepared as an addition reaction-type organopolysiloxane(release agent composition E) having a weight-average molecular weightof 634,000. A release sheet was produced in the same manner in Example 1except that the release agent composition E was used in place of therelease agent composition A in Example 1.

Comparative Example 1

a mixture of phenyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 400,000) as the first polydimethylsiloxane andpolymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, was prepared as an additionreaction-type organopolysiloxane (release agent composition F) having aweight-average molecular weight of 344,000. A release sheet was producedin the same manner in Example 1 except that the release agentcomposition F was used in place of the release agent composition A inExample 1.

Comparative Example 2

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin, was prepared as an addition reaction-type organopolysiloxane(release agent composition G) having a weight-average molecular weightof 440,000. A release sheet was produced in the same manner in Example 1except that the release agent composition G was used in place of therelease agent composition A in Example 1.

Comparative Example 3

A mixture of vinyl-modified silicone resin having at least two vinylgroups in the structure of polydimethylsiloxane (weight-averagemolecular weight: 1,100,000) as the first polydimethylsiloxane,polymethylhydrogensiloxane having at least two hydrosilyl groups in thestructure of polydimethylsiloxane (weight-average molecular weight:1,000) as the second polydimethylsiloxane, and vinyl-modified siliconeresin having at least two vinyl groups in the structure of siliconeresin, was prepared as an addition reaction-type organopolysiloxane(release agent composition H) having a weight-average molecular weightof 696,000. A release sheet was produced in the same manner in Example 1except that the release agent composition H was used in place of therelease agent composition A in Example 1.

<Exemplary Test 1>

Each amount of the functional groups (vinyl groups/hydrosilyl groups) inthe release agent compositions A to H used in the examples and thecomparative examples was measured in accordance with the measuringmethod as below.

Deuterated chloroform (available from KANTO CHEMICAL CO., INC., puregrade of 99.8%) was added to a sample of polydimethylsiloxane so thatthe solid content of the sample of polydimethylsiloxane would be 10 mass%; pyrazine (PO554 available from Tokyo Chemical Industry Co., Ltd.) wasadded thereto so as to be of 0.3 mass % with respect to the sample ofpolydimethylsiloxane; and the mixture thus obtained was put into an NMRtube. For the sample put into the NMR tube, NMR measurement wasperformed using a nuclear magnetic resonator (NMR-Fourier 300 availablefrom BRUKER CORPORATION) to quantitatively determine each amount (mmol)of the functional groups, i.e., each amount of vinyl groups andhydrosilyl groups.

From the measurement results as the above, a molar ratio (b/a) of thehydrosilyl groups (b) to the alkenyl groups (a) was calculated.Respective results are listed in Table 1.

<Exemplary Test 2>

In a clean room under a condition of class 10,000 (ISO class 7), atemperature of 23° C. and a humidity of 50% RH, the release sheetobtained in each of the examples and the comparative examples wassuspended in the vertical direction to the ground surface, and exposedto the air for 1 day or 7 days.

Under a condition of a temperature of 23° C. and a humidity of 50% RH, apolyester pressure sensitive adhesive tape (available from NITTO DENKOCORPORATION, item number: No. 31B, width of 20 mm) was applied to thesurface of the release agent layer of each of the release sheets withoutexposure to the air and the above release sheets exposed to the air byreciprocating a roller of 2 kg once, and a test piece for peeling forcemeasurement was thus obtained.

After 30 minutes elapsed from the application of the polyester pressuresensitive adhesive tape, the peeling force was measured for the obtainedtest piece. A tensile tester available from SHIMADZU CORPORATION (itemnumber: AG-IS 500N (load cell: 20 N)) was used to measure the peelingforce. Specifically, the side of the release sheet of the sample wasfixed to a SUS plate; the polyester pressure sensitive adhesive tape waspeeled off at a speed of 0.3 m/min while being bended at 180°; and thepeeling force (mN/20 mm) at that time was measured. From the peelingforce thus obtained, the peeling force rate of change (%) was calculatedin accordance with the following equation:peeling force rate of change (%)={(peeling force Y−peeling forceX)/peeling force X}×100,wherethe peeling force X: peeling force without exposure to the air, andthe peeling force Y: peeling force exposed to the air for 1 day or 7days.The results are listed in Table 2.

TABLE 1 Amount of functional groups (mmol) Hydrosilyl Molar ratio Vinylgroups (a) groups (b) (b/a) Example 1 11.36 141.53 12.5 Example 2 13.2297.12 7.3 Example 3 14.66 70.23 4.8 Example 4 15.21 57.23 3.8 Example 515.80 43.41 2.7 Comparative 10.80 20.10 1.9 Example 1 Comparative 9.96174.98 17.6 Example 2 Comparative 15.81 35.32 2.2 Example 3

TABLE 2 Peeling force rate Peeling force (mN/20 mm) of change (%)Exposed Exposed Exposed Exposed Without for 1 for 7 for 1 for 7 exposureday days day days Example 1 233 196 176 −16 −24 Example 2 143 118 116−18 −19 Example 3 118 101 104 −14 −12 Example 4 107 94 101 −12 −5Example 5 85 97 107 15 27 Comparative 46 477 910 937 1878 Example 1Comparative 343 293 236 −15 −31 Example 2 Comparative 52 92 134 78 158Example 3

As apparent from the results listed in Table 1 and Table 2, the releasesheets using the release agent compositions satisfying the requirementsof the present invention showed a much smaller peeling force rate ofchange due to exposure to the air.

INDUSTRIAL APPLICABILITY

The release sheet according to the present invention is suitably used asa release sheet of which the release agent layer is to be exposed to theair for a long time, such as for being subjected to back-splitprocessing.

DESCRIPTION OF REFERENCE NUMERALS

-   1 . . . Release sheet-   11 . . . Base material-   12 . . . Release agent layer

The invention claimed is:
 1. A release sheet comprising: a base materialand a release agent layer formed on at least one surface of the basematerial, wherein the release agent layer is formed by using a releaseagent composition; the release agent composition contains a firstpolydimethylsiloxane having at least two alkenyl groups in one moleculeand a second polydimethylsiloxane having at least two hydrosilyl groupsin one molecule; the release agent composition contains 10.00 to 16.00mmol of the alkenyl groups and 40.00 to 145.00 mmol of the hydrosilylgroups in a total of 30 g of the first polydimethylsiloxane and thesecond polydimethylsiloxane; and a molar ratio (b/a) of the hydrosilylgroups (b) to the alkenyl groups (a) is 2.5 to 14.5.
 2. The releasesheet as recited in claim 1, wherein a weight-average molecular weightof the first polydimethylsiloxane is 200,000 to 1,300,000 and aweight-average molecular weight of the second polydimethylsiloxane is300 to 1,200.
 3. The release sheet as recited in claim 1, wherein therelease agent composition further contains a platinum-group metal-basedcompound as a catalyst.
 4. The release sheet as recited in claim 1,wherein a peeling force rate of change represented by {(peeling forceY−peeling force X)/peeling force X}×100 is 30% or less, where thepeeling force X is a 180° peeling force (mN/20 mm) of a polyesterpressure sensitive adhesive tape No. 31B available from Nitto DenkoCorporation from the release sheet in a state of no exposure to air, andthe peeling force Y is a 180° peeling force (mN/20 mm) of a polyesterpressure sensitive adhesive tape No. 31B available from Nitto DenkoCorporation from the release sheet which has been exposed to air for 7days in a clean room under a condition of class 10,000 (ISO class 7), atemperature of 23° C. and a humidity of 50% RH.
 5. The release sheet asrecited in claim 2, wherein the release agent composition furthercontains a platinum-group metal-based compound as a catalyst.
 6. Therelease sheet as recited in claim 2, wherein a peeling force rate ofchange represented by {(peeling force Y−peeling force X)/peeling forceX}×100 is 30% or less, where the peeling force X is a 180° peeling force(mN/20 mm) of a polyester pressure sensitive adhesive tape No. 31Bavailable from Nitto Denko Corporation from the release sheet in a stateof no exposure to air, and the peeling force Y is a 180° peeling force(mN/20 mm) of a polyester pressure sensitive adhesive tape No. 31Bavailable from Nitto Denko Corporation from the release sheet which hasbeen exposed to air for 7 days in a clean room under a condition ofclass 10,000 (ISO class 7), a temperature of 23° C. and a humidity of50% RH.
 7. The release sheet as recited in claim 3, wherein a peelingforce rate of change represented by {(peeling force Y−peeling forceX)/peeling force X}×100 is 30% or less, where the peeling force X is a180° peeling force (mN/20 mm) of a polyester pressure sensitive adhesivetape No. 31B available from Nitto Denko Corporation from the releasesheet in a state of no exposure to air, and the peeling force Y is a180° peeling force (mN/20 mm) of a polyester pressure sensitive adhesivetape No. 31B available from Nitto Denko Corporation from the releasesheet which has been exposed to air for 7 days in a clean room under acondition of class 10,000 (ISO class 7), a temperature of 23° C. and ahumidity of 50% RH.